1. Field of the Invention
The present invention relates to a method and apparatus for the production of glass fibers.
2. Background of the Invention
Apparatus for the production of glass fibers, such as for use in reinforcing plastics, or the production of elongated glass filaments, are known. In general, a molten glass mass is prepared in a furnace or the like and fed to a forechamber acting as a reservoir which is provided with one or more nozzles or nozzle plates through which the glass mass is extruded by gravity. Apparatus of this type is described in German Publication DT-AS No. 1158671.
Although the extrusion of the glass mass is effected by gravity, the known apparatus has the disadvantage that the forechamber can operate only with a glass mass column of only 200 to 250 millimeters above the nozzle plate. Known nozzle plates through which the molten glass is drawn comprise for example, a trough-type vessel of a platinum alloy which is provided with nozzles or nozzle tips, from which the molten glass can issue. The nozzle plate is connected as a resistance in a low voltage circuit and is thus electrically heated to maintain the molten glass contained therein in its molten state. Such vessels have the significant disadvantage that the temperature of the molten glass has a random characteristic as the temperature of the trough walls has a temperature gradient which decreases toward the upper edge leaving the highest temperature just above the bottom surface of the trough itself.
Due to the irregular temperature, additional turbulence results within the molten glass mass leading to frequent filament breaks and ruptures as well as the formation of irregular filament diameters.
It is also known that the glass mass in the forechamber must be heated to at least 1350.degree. C., although the use of the conventional burners, in order to obtain at the nozzle, a useful operating temperature of 1240.degree. C. These parameters limit the height of the glass column above the nozzles to no more than about 250 millimeters, as otherwise the temperature of the glass mass would have too strong a temperature gradient. On the other hand, it is known through the Hagen-Poiseuille equation, that a higher glass column or head producing a higher hydrostatic pressure above the nozzle plate, causes an increased flow rate and, hence, increased efficiency of the apparatus. The Hagen-Poiseuille equation is ##EQU1## where: Q is the flow rate, per unit time,
K is a constant, PA1 H is the height of the glass mass above the nozzle plate PA1 D is the diameter of the nozzle tip PA1 N is the number of orifices in the nozzle plate PA1 v is the viscosity of the molten glass, and PA1 L is the length of the nozzle tip.
3. Object of the Invention
It is an object of the present invention to provide a method of and an apparatus for the production of glass fibers wherein the flow rate can be significantly increased, the quality of the fibers optimized, and the subsequent treatment process further reduced or eliminated. Under certain conditions, even direct roving filaments can be produced.